1. Field of the Invention
This invention relates to a process for the production of high-chromium steel by the smelting reduction of chromium oxide, such as chromium ore, by using a solid carbonaceous substance, such as coke, as a combination heat source and reducing agent instead of using electric power as a heat source. The term "high-chromium alloy" as used in this invention means an alloy formed preponderantly of Cr--Fe--C and used as a chromium source for the production of high-chromium steel. Because of the function to be fulfilled as a chromium source, this alloy is required to have a chromium content of not less than 17%.
2. Description of the Prior Art
Heretofore, the high-chromium alloy such as, for example, ferrochromium having a chromium content of at least 50% has been produced by heating, melting, and reducing chromium ore or partially reduced chromium ore as disclosed in Japanese Patent Application Laid-open SHO No. 52(1977)-138418, for example. This process, however, has entailed the following problems.
(1) The cost of production is high because expensive electric power is used as reducing energy. PA0 (2) The slag discharged from the furnace has a high chromium content of 2 to 5%, indicating the process to involve a heavy loss of chromium. Further, since the slag has such a high chromium content, it finds utility in a limited range of applications. PA0 (1) The smelting reduction process must rely upon the heat of the oxidation of a carbonaceous material for supply of the energy for heating and melting raw materials and reducing oxides. For the amount of heat generated per the amount of the carbonaceous material to be improved, not only the reaction of C.fwdarw.CO but also the reaction of C.fwdarw.CO.fwdarw.CO.sub.2 is desired to be utilized to the fullest extent. In other words, for efficient generation of heat, the atmosphere must be reduced oxidative. What measure, then, has to be taken to satisfy simultaneously this requirement and the requirement that the reduction should be made to proceed to the extent of amply lowering the chromium content in the slag? PA0 (2) Since the chromium component in the chromium ore forms spinel which is sparingly fusible, the melting of the chromium ore and the reduction of the chromium component proceed at low rates of speed. Further, since the chromium ore contains such oxides as MgO, Al.sub.2 O.sub.3, and SiO.sub.2 in large amounts, the amount of the slag produced in the process is very large. What measure, then, has to be taken to promote the reaction which is thus expected to proceed at a low rate of speed? PA0 (3) The conventional low shaft electric furnace is advantageous in respect that the hot temperature part due to the heat of the arc and the furnace wall are isolated from each other by the melt filling the furnace and that the lining forming the furnace wall is consumed only sparingly because the melt generates virtually no flow near the furnace wall. In contrast to the smelting fusion process, since the degree of heat concentration is low, the load upon the lining is increased when the melt is stirred hard or the overall temperature of the reaction part is elevated for the promotion of the reaction. What measure, then, has to be taken to curb injury to the lining?
Japanese Patent Application Laid-open SHO No. 50(1975)-108116 discloses a process for the production of low-carbon chromium-containing steel and ferrochromium alloy from a high-carbon chromium-containing alloy by supplying oxygen or oxygen-containing gas into a molten metal covered with slag through at least one nozzle located beneath the level of the molten metal, which process is characterized in that, in order to decrease slaglization of chromium, a finely divided solid carbon carrier is supplied into the molten metal through one or more additional nozzles which belongs to the aforementioned oxygen nozzle, in such a manner that the carbon carrier encases the stream of oxygen.
The prior art, however, has not yet produced any effective means of causing the smelting reduction of chromium oxide such as chromium ore without use of electric power.